1. Field of the Invention
The present application relates to a transmitting optical module, in particular, a transmitting optical module implementing with a planar light wave circuit (PLC) for multiplexing optical signals.
2. Background Arts
Recently, transmit ing optical modules are requested to be operable in high frequencies exceeding 40 Gbps, or sometimes reaching 100 Gbps, to enhance the communication capacity in an optical communication system. In such a high speed transmission, an optical signal that multiplexes a plurality of sub-signals each having wavelengths different from each other that is, the wavelength division multiplexing (WDM), becomes popular.
One example of a transmitting optical module applicable to such a WDM system has been disclosed in the U.S. Pat. No. 8,625,989, in which a transmitting optical module installs four semiconductor laser diodes (LDs) and multiplexes optical signals output from respective LDs. The transmitter optical module disclosed therein multiplexes the optical signals by a plurality of lenses, mirrors, wavelength selective filters (WSFs), and a polarization beam combiner (PBC). On the other hand, another transmitting optical module that multiplexes a plurality of optical signals by a planar lightwave circuit (PLC) including optical waveguides has been also known in the field.